Spectroscopy refers to determining the nature of a substance by measuring a parameter of energy emitted by the substance. For example, if a laser beam is scattered off of a substance, most of the photons will be elastically scattered (that is, their wavelength will remain the same) but some will be inelastically scattered (their wavelength be changed as a result of an exchange of energy between the incident photons and the molecules of the substance. This change of wavelength is called the Raman Effect. The substance can be identified by measuring how much the wavelength has shifted. The Raman Effect can be enhanced by adsorbing molecules of the substance onto a rough metal surface and then exposing them to the incident laser beam. This technique is referred to as surface-enhanced Raman spectroscopy (SERS). The enhancement factor is so high—as much as 1011—that individual molecules of the substance can be identified. A suitable surface may be prepared by forming tiny projections called nanofingers on a silicon substrate; in some instances, tips of the nanofingers are thinly coated with a metal such as gold or silver. When an unknown substance is adsorbed onto the surface, capillary action causes the nanofingers to bend toward each other, trapping individual molecules. The nanofingers may be thought of as tiny tweezers that hold these individual molecules of the unknown substance up to the laser beam for analysis. When the laser beam is scattered off of the nanofingers, it is directed through a precision optical path that includes various optical components including a filter to attenuate any elastically-scattered photons and then to a photodetector such as a charge-coupled device (CCD). The photodetector provides a signal that is analyzed to determine the wavelength shift and thereby identify the substance.